My low thrust probe in Jool orbit is cursed

[Darta01]

Hi all, it's the first time I post on this forum, even if I regularly come here to read comments since v0.1 launch. But I need to express my frustration on the mission I am trying to conduct.

After unlocking the ion engine in my exploration mode playthrough, I sent a Cassini-like probe toward Jool. It weighs 3.6t, and has a secondary probe meant to dive into Jool's atmosphere in order to accomplish the Lens Test mission. It has two "Dawn" ion engine, with only one activated at first, that is aligned to the center of mass of the combined probe. And it has two "Gigantor" solar arrays. Since the probe has a lot of ΔV (around 11km/s), I sent it on a fast transfer, and it arrived with more than 6600m/s of velocity at Jool encounter. The capture burn is of course very long (approx. 21h with one engine at full power), but KSP2 now allows to accelerate under time warp, which is a great improvement from KSP1.

Being so far from Kerbol, each solar array provides only ~0.5Ec/s, and the engine uses 10Ec/s at full power. That is not really a problem when accelerating under time warp: I set the engine's thrust level to 20% in the part manager in order to have a better control on the throttle, and then throttled to 50%. By doing this just after entering Jool's SOI, the probe has 27 days before arriving at periapsis, wich is enough to perform a capture burn. But now the trouble began. The acceleration did not work under time warp. The trajectory was effectively changing without time warp, but not with it.

It is not my first probe around Jool in this playthrough in KSP 2 v0.2.x, but the first ionic one, and it is also the first time I encounter this bug. I did the usual: reloading the save, quitting and reloading the game, but nothing changed. After some search on forums, I found that this bug sometimes occur with low-thrust probes having a maneuver node set, so I deleted my capture maneuver node (it was useless anyway), but again nothing changed.

After some manipulations, It appears that it does not really depend on the engine throttle, but on the spacecraft acceleration. I tried various combinations of the engine thrust level and main throttle. When the engine is at 10% power the acceleration does not work under time warp, but above 25% it does. There must be an acceleration threshold under which the game considers the spacecraft to be in free fall and does not compute the acceleration, placing the probe on a fixed trajectory under time warp. So, it's not a bug, it's a feature! The threshold is just too high for a low-thrust probe, and I was not even trying to test the game's boundaries...

 

Since I was not ready to let my computer run 200h to perform the capture burn at normal warp speed, I tried another approach. I set the engine at 25% thrust, accelerated under time warp until electricity depletion, stopped time warp, cut the throttle, time warpped until the batteries were fully recharged, and repeated... One cycle of this manipulation allows to perform 20m/s of ΔV. So 300 cycles were needed. Less than 200h playing, but still several hours...

So, to preserve my sanity, I decided to activate the cheats, a thing I did not do since v0.9 of KSP1. I activated Infinite Electricity, activated both engine, set them to 100% thrust level, pushed the main throttle to 100% and... gasped, as I saw the electricity being drained at an alarming rate. So it appears the Infinite Electricity cheat does not make the electricity infinite! I thought it was a bug (again!), but in fact I had to activate Infinite Fuel cheat in order for the engines not to consume electricity. So, it's not a bug, it's a feature! Joke appart, I think it is a UI/UX default, first because electricity is not part of the fuel of an electric engine, at least not in the common sense of engine fuel; and second because a player checking Infinite Electricity would expect it to do what is said.

 

So, back to my probe. I activated both cheats, and started to perform the capture burn under time warp. All was going well (well, except for the above mentionned bugs), the hyperbolic trajectory was closing. I reduced the warp speed when the probe approached a parabolic trajectory because I wanted to finely control the altitude of the apoapsis. But then, the apoapsis decreased until reaching a value of approximately -900k or -900M km, I don't remember correctly, and then suddenly stopped. The trajectory was, again, not changing.

I was starting to be very upset. I tried again to quit and reload the game, but now the apoapsis shows 0m, and I am still unable to do any change on the trajectory, wichever the direction of thrust. My probe is forever stuck on an escaping, parabolic trajectory. I guess the Kraken really does not want me to orbit Jool! Maybe it is hiding something on one of its moons...

 

Is this last issue common? Does someone have a workaround?

I can still load an earlier save and try and perform the capture burn again I guess. But for now I'm a bit tired, after all the time spent on this situation. I'm litterally at the edge of achieving the capture!

[The Aziz]

The sole fact that you were brave enough to try a Dawn-based probe on Jool...

But also

 

[Darta01]

9 hours ago, The Aziz said:

The sole fact that you were brave enough to try a Dawn-based probe on Jool...

Well I didn't read the bug reports before playing this mission, so it was an obvious solution to me for a Jool-5 capable probe. Too bad this propulsion technology is not ready yet in this game. I've been reading the KERB updates, and they talk about acceleration under time warp bugs, but without specifically pointing the Dawn engine

9 hours ago, The Aziz said:

But also

 

Thank you for the link. From my uninformed point of view, there seem to be multiple unrelated bugs affecting ion engines and time warp. I will read the full thread when I'll have the time, and maybe I'll share my save. It might help the devs and the QA dep.

[The Aziz]

2 hours ago, Darta01 said:

, so it was an obvious solution to me for a Jool-5 capable probe

Hydrogen. With payload light enough you can easily get a Jool5 capable ship. And you're not limited by solar power (though obviously there are other means of electricity generation). Using xenon at full power is pretty much impossible past Dres if you rely on solar panels.

[kdaviper]

I had the same bug happen to me today with a lower TWR hydrogen engine-powered craft so I think this must be some kind of rounding error.

Strange how accel under timewarp doesn't work in the cases it would be most useful

Edited February 14 by kdaviper